This invention relates generally to methods and apparatus for electronic data entry and more particularly to methods and apparatus for matrix or touch-screen keyboard control.
In at least one known configuration of an industrial controller or computer, a matrix keyboard or matrix touch screen is scanned continuously to determine whether a key has been pressed. This scanning can be done either via software or hardware polling. Whichever type of polling is used, this configuration requires that a debounce period be determined and a debounce algorithm be developed to prevent data from the keyboard from being contaminated with unintended multiple signaling of each keypress. For matrix keyboards and matrix touch screens from different manufacturers, circuit impedance varies. This variable impedance results in variable rise and fall times of make and break signals, thus requiring different debounce periods.
Some industrial applications require support for a “jog” function, i.e., a “jog key” is provided that controls movement of a motor while the “jog” key is held down. In known keyboard control systems that provide a jog function, this function is provided by software that constantly polls the state of the keys on the keyboard. This polling increases the load on the controller and tends to make it less responsive. Also, when a key is held down, the software remains responsive to other keys on the keyboard. If the user or a nearby person happens to press or another key while one key is held down or fumble while attempting to press a particular key, all of the keys that are hit or held down eventually are eventually read by the software program interpreting the input keystrokes. The erroneously activated keys may cause unintended and/or unpredictable consequences in the operation of an industrial device.